The beneficial effect of zinc compounds in dental compositions, especially in toothpastes and mouthwashes, has been generally recognized for some time. In U.S. Pat. No. 4,100,269, issued July 11, 1978 to Morton Pader, there is disclosed the use of insoluble zinc compounds in dentifrices for improving the control of calculus. Insoluble zinc compounds employed in the patent are those having a solubility of less than about one gram of zinc per 100 cc of water at 20.degree. C. and preferably a solubility of not more than about 0.5 gram zinc compound per 100 cc water at 20.degree. C. Among the typical insoluble zinc compounds employed in the patent is zinc citrate. In U.S. Pat. No. 4,138,477, issued Feb. 6, 1979, to Maria Gaffar, there is disclosed composition for preventing and controlling mouth odor containing a zinc-polymer combination of a zinc compound and an anionic polymer. Also it has been known to formulate tooth powders containing zinc citrate and calcium gluconate such as disclosed in U.S. Pat. No. 1,861,189 issued May 31, 1932 to Charles Pfizer.
In addition, zinc chloride has been used in mouthwash compositions and recognized as possessing anti-mouth odor properties in said compositions. In U.S. Pat. No. 2,527,686, issued Oct. 31, 1959, to Max Sandberg, a mouthwash containing zinc chloride and an alkali metal or ammonium fluoride which also contains papain, malt and formalin is disclosed. However, the zinc chloride is not really very stable in such a formulation and the necessity to include formalin, papain and malt is not desirable. Moreover, a zinc chloride mouthwash is stable only at an acid pH of about 3.
However, despite the heretofore known use of zinc compounds in dental compositions their use has not been without certain undesirable drawbacks and side-effects. For example, when such zinc compounds have been employed it has not been possible to satisfactorily include ionic fluoride in the compositions due to the chemical incompatibility therebetween. A sodium fluoride mouthwash must have a pH in the neutral range since at acidic pH the enamel solubility of teeth is increased resulting in increased tooth decay. Moreover, while zinc chloride possesses the desired anti-odor activity, its high level of astringency is undesirable. Yet other zinc compounds, such as for example, zinc citrate are so slightly soluble in aqueous solutions that while the level of astringency is kept acceptably low, there is an undesirable loss in anti-mouth odor activity of the zinc compound.
It is therefore highly desirable to provide a mouthwash composition that is less astringent than zinc chloride so as to provide enhanced acceptance by users of dental compositions containing same yet without sacrificing anti-odor activity. It is also desirable to provide a stable mouthwash composition containing a zinc compound not as astringent as zinc chloride but which does not present substantially any chemical incompatibility problem in dental compositions employing an ionic fluoride compound.